Method for the preparation of an overglaze ceramic decalcomania

ABSTRACT

A method for the preparation of an overglaze ceramic decalcomania is provided wherein a wet ink formulation containing a liquid printing vehicle or medium and an oxide coloring agent, free of glass, is wet printed on a decalcomania backing sheet to form a wet design layer thereon free of glass, and a protective coating of prefused glass flux is separately deposited on the wet design layer, so that when the design layer and protective coating deposited thereon is positioned on a glazed piece of ware and fired, the protective coating of prefused glass flux fuses and tightly binds the design layer to the ware.

United States Patent Blanco METHOD FOR THE PREPARATION OF AN OVERGLAZECERAMIC DECALCOMANIA Inventor:

Assignee:

Filed:

Louis A. Blanco, Tuckahoe, N.Y.

Commercial Decal, 1nc., Mt.

Vernon, NY.

Oct. 27, 1971 U.S. Cl 11713.1, ll7/3.6, 117/13,

Int. Cl B4lm 3/12, B4lm 7/02 Field of Search 117/62, 13, 3.1-3.6,

117/70 A, 70 C, 70 S, 40, 45, 23, 25

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS278,801 10/1927 Great Britain 117/25 6,548 5/1887 Great Britain....117/13 117,216 7/1943 Australia 117/13 Primary Examiner-William D.Martin Assistant Examiner-Harry J. Gwinnell AttorneyLawrence I. Lerner[57] ABSTRACT A method for the preparation of an overglaze ceramicdecalcomania is provided wherein a wet ink formulation containing aliquid printing vehicle or medium and an oxide coloring agent, free ofglass, is wet printed on a decalcomania backing sheet to form a wetdesign layer thereon free of glass, and a protective coating of prefusedglass flux is separately deposited on the wet design layer, so that whenthe design layer and protective coating deposited thereon is positionedon a glazed piece of ware and fired, the protective coating of prefusedglass flux fuses and tightly binds the design layer to the ware,

6 Claims, No Drawings METHOD FOR THE PREPARATION OF AN OVERGLAZE CERAMICDECALCOMANIA BRIEF SUMMARY OF THE INVENTION The present inventionrelates to a method of preparing an overglaze ceramic decalcomania ordecal by wet printing a design layer, free of glass, on a backing sheetand separately depositing a protective coating of prefused glass flux onthe wet design layer.

BACKGROUND OF THE INVENTION A decal usually is comprised of amulti-layer structure including a backing, a design layer and aprotective layer applied over the design layer. The colors in the designlayer are formed from inorganic pigments or oxides. A layer facilitatingrelease of the backing from the design may be interposed between thebacking layer and the design layer.

A number of different types of decals are used at present in the potteryindustry to apply patterns to ceramic ware. One of these is theso-called underglaze decal. This type of decal is applied to the wareafter the ware has been formed but before it is glazed. Thereafter, aglaze is applied over the ware and decal. This glaze consists of avitreous coating. The coating is formed directly from raw materials sothat a very high temperature must be used in firing the ware to form theglass. The result of this process is a protective coating over thepigment such that the pigment will not be subject to chemical andmechanical attack such as produced by modern chemical detergents andmechanical washing devices. However, the use of such a high temperatureas is necessary to form the glaze destroys the color value of many ofthe pigments that would be preferred to produce the desired colors. Inaddition, the glaze may be somewhat opaque so that the designs of thedecal are obscured. It will be appreciated from the foregoing that thisunderglaze ceramic decal is limited in application.

As a result of these limitations, the so-called overglaze" decals weredeveloped. That is, decals which are applied to the ware after the hightemperature glaze has been put on. These overglaze decals can generallybe divided into two classes silk screen decals and lithographic decals.

In the silk screen process a silk screen template or stencil is placedover the surface on which pigment is to be deposited and the pigmentapplied through the screen. If the decal were of the water mount orslide off type, the surface on which the pigment is applied would be thelayer of water soluble gum which has been placed over a paper backing.In this process a relatively thick layer of pigment is deposited overthe entire surface covered by the stencil. In order to increase thepennanence of the design in the silk screen decal, a quantity ofpowdered low melting point glass may be mixed with the pigment so thatwhen the pattern is set by the application of heat this powdered glasswill fuse and become a part of the pattern itself. The silk screendecals, however, like the underglaze decals, are subject to a number oflimitations. For example, the fine and clear cut designs and tonalvariations available in the lithographic process cannot be obtained bythe silk screen process. Also, the thicker pattern which results fromthis process is not always desirable. Because of these limitationslithographic decals are widely used in the industry.

Lithographic decals are formed by printing a layer of the desiredpattern for one pigment in a clear varnish and then dusting the pigmentover the entire sheet in a lithographic process. The sheet is thencleaned leaving pigment only where the varnish is. The sheet is thenpermitted to dry. If other colors are desired, the foregoing processmust be repeated for each color. It will be appreciated that a largeproportion of pigment is wasted in this process because it is dustedover the entire sheet and a great deal is not recovered in the cleaningprocess. A great deal less is required in the method of the presentinvention because pigment is only printed on these areas where it isdesired.

Kane, U. 8. Pat. No. 2,734,840, discloses a lithographic decal which isstrongly resistant to chemical and mechanical attack and which is madeby dusting a mixture of powdered glass and solid pigment powder or solidpigment globules on a backing sheet containing an adhesive such as a gumor varnish to form a dry design layer thereon and thereafter coveringthe pigment-glass design layer with a layer of powdered low meltingpoint glass. Conventional wet printing techniques such as offsetprinting cannot be employed to form the dry design layer disclosed byKane. If the pigment-glass mixtures of Kane are employed in a wetprinting medium, the presence of the glass with the pigment dilutes thecolor value of the pigment. Excessively large amounts of pigment wouldbe required to compensate for color dilution, the result of which wouldbe the formation of excessively thick design layers, which serve nouseful purpose. In addition, spreading of the color by means of printingrollers, employed in wet printing techniques, is difficult because ofthe present of relatively large glass particles.

British Pat. No. 1,094,104 to Johnson, Matthey & Co. discloses a ceramicpigment transfer and method for making the same wherein an inkcomprising a printing medium or varnish incorporating a ceramic pigmentis applied to a backing sheet and a covering layer of anadhesion-promoting flux of glass-forming constituents is applied overthe pigment layer. The covering layer is adapted to fuse to form anouter protective layer when fired. The flux of glass-formingconstituents is said to include constituents adapted to form aleadborosilicate glass, such as lead oxide, boric acid and silica.

It has been found that where glass-forming constituents, such as leadoxide, boric acid and silica, are coated on the pigment layer and fired,these glassforming constituents each have a different melting point andtherefore melt at different times on the pigment layer, causing thepigment layer to become spotty. It is only after all of theseglass-forming constituents melt and chemically react that glass is, infact, formed. However, by this time it is too late and the design isalready discolored. The problem of discoloration of the design orpigment layer is inherent in the process of this British patent.

Lawrence, U. S. Pat. No. 2,008,763, discloses a transfer or decalsubstitute wherein a design is applied to a base by means of a markingcomposition comprised in gum dammar parts), castor oil (20 parts),kerosene (40 parts) and boiled linseed oil (20 parts) and which cancontain a metallic pigment. After the marking is applied to the base,the marking may be dusted with a non-fusible bronze powder which clingsto the moist design. The marking is then allowed to dry at roomtemperature by evaporation of the kerosene. The transfer therebyproduced has the inherent limitation that the non-fusible bronze powderlayer could mask or interfere with the marking if a metallic pigmentother than bronze is employed in the marking. These decals are notceramic decals.

OBJECTS It is, accordingly, an object of the present invention toprovide an improved method for printing a decal. Another object is toprovide a method for forming an improved overglaze decal which requiresless pigment. Still another object is to provide a faster, moreeconomical method for preparing a decal. A further object is to providean improved method for applying a flux layer to the design layer of adecal. These and other objects of the present invention will be apparentfrom the following description.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the presentinvention, there is provided a method for the preparation of anoverglaze ceramic decalcomania, which comprises forming a wet inkformulation free of glass and comprising an oxide coloring agent and aliquid printing medium or vehicle such as a drying oil, varnish orresin, wet printing the wet ink formulation on a decalcomania backingsheet to form a wet design layer thereon free of glass, and separatelydepositing on the wet design layer a protective coating in the form of aprefused glass flux. lf desired, the prefused glass flux layer may beinitially deposited on the backing sheet and the wet design layer wetprinted on the glass layer. When the backing sheet containing the wetdesign layer and protective coating is positioned on a glazed piece ofware and fired, the protective coating of prefused glass flux fuses andtightly binds the design layer to the ware.

When wet printing the wet ink formulation on the decalcomania backingsheet, a relatively thin design layer is formed which may be of anycolor of any desired intensity. The design layer should have a thicknesswithin the range of from about 2 to about 8 microns and preferably fromabout 2 to about 6 microns.

The wet design layer can be formed in accordance with the inventionemploying only a fraction (for example from one-twentieth to one-fifth)of the pigment as would be required in prior art processes wherein dryor solid pigments plus glass is employed to obtain the same intensity ofcolor as obtained in such processes. Accordingly, the use of wetprinting results in a process which is far and away more efficient thanprior art processes as exemplified by the Kane patent mentionedheretofore.

The prefused glass flux protective layer is colorless so that it doesnot interfere with or mask the colors of the design layer. The prefusedglass flux may include a metallic oxide. The metallic oxide would bepresent in an amount within the range of from about 1 to about 8 percentby weight.

An amount of the prefused glass flux should be deposited on the wetdesign layer so that the protective glass coating thereafter formed willhave a thickness within the range of from about 6 to about 28 micronsand preferably from about 9 to about 20 microns. Thus, the ratio ofthickness of the glass protective coating to the design layer should bewithin the range of from about 2:1 to about 3.5:] and preferably fromabout 2:1 to about 2.521.

The decal of the present invention may be provided with any suitablebacking, such as a dry strippable backing or a solvent mount or a watermount slide-off decal. The backing may be of paper or other suitablematerial such as, for example, plastic or fabric.

The wet design layer may be applied to the backing as one or more layersof an ink comprising an oxide colorant and a printing medium or vehiclewithout a glass flux or binder. The ink should contain from about 30 toabout 60 percent by weight and preferably from about 35 to about 45percent by weight oxide colorant. The printing medium or vehicle may beformed, for example, from one or more of such materials as drying oils,varnishes, or resins. Some examples of suitable resins are alkyds,phenolics, urea-formaldehydes, melamine-fonnaldehydes, polyesters,melamine alkyds, vinyls, and acrylics. Various additives may beincorporated into the vehicles, for example, dryers, promotors, and/oraccelerators.

The coloring agents of the design layer comprise ceramic pigments,having an average particle size within the range of from about 0.5 toabout 2 microns which are incorporated into the binder or vehicle.Preferably, the pigments are metallic oxides of fine particle size, suchas of an average particle of less than about 1 micron. The pigmentswhich may be used and the manner of their use are known to those skilledin the art. The oxides of the following elements are mentioned merely byway of example of some suitable ceramic pigments and the colorsobtainable therefrom:

Oxide of Color Fe, Cr, Zn Brown Co, Al Blue Cr Green PB, Sb, Cd YellowCd, Se, S Red ingredient l Gel #1 00 (linseed-alkyd resin varnish gelledby aluminum octoate, supplied by Zobel Co.)..... 10 I2 Linseed #4(linseed oil of 62.1 stokes viscosity) Linseed #1 (linseed oil of 14 4stokes viscosity). Lead drier Manganese drier. Oxide (pigment). Aroplaz2506 (alkyd resin supplied by Archer- Daniels) 30 25 Aroplaz 1274 (alkydresin supplied by Archer- Daniels) 30 25 Puffo #2 (thixotropic controlagent supplied by Mooney) 3 3 Petroleum jelly 5 The coating or layeror'bowiird'giatshaybea law melting point glass or a high melting pointglass having an average particle size within the range of from about 4to about 12 microns. The essential requirement is that the glass wouldfuse at the firing temperature employed to bond the design to the ware.A low melting point glass may be composed essentially of powderedpre-fused lead boro-silicate glass which may also contain increments ofone or more of the oxides of lithium, sodium, potassium, magnesium,calcium, aluminum, cadmium, zirconium or titanium.

A pre-fused flux may, for example, be formed according to the followingformulation:

INGREDIENT BY WEIGHT lead oxide 50 boric acid 30 silica l9 alumina lzirconia trace titania trace According to the present invention new andimproved printing procedures are obtainable. It is possible to wet printthe design according to conventional printing techniques such as byscreen printing or offset lithography and then to apply over the wetdesign a prefused glass flux to permit fusion of the design to a ceramicsurface. The flux may be applied over the design by various methods,such as, silk screening, offset printing, or by printing a clear filmover the design and then dusting a prefused flux over the film. Ifdesired, the dusting operation may be eliminated by incorporating theflux into film such as a printing varnish, oil or resin.

It is also possible to print the design as above and to dust a prefusedflux over each color as each color is printed. In this way a separatestep of applying flux over the entire design is eliminated. The fluxthat is picked up by the tacky varnish will enable the ceramiccalcinedpigment to fuse to the ceramic surface. This procedure also preventsofisetting of the ink when the printed designs are stacked or piled ontop of one another.

It is also possible to print a prefused flux (either as a dust or as amoist coating) on an adhesive-coated paper, such as paper coated withgum arabic and dextrin. The flux coated paper is then overprinted withthe pigmented vehicle or design. It is then possible, if desired tooverprint the design with another flux whereby the design is sandwichedbetween two flux prints.

It is also possible to silk screen a white color on an adhesive-coatedpaper and then to print the design, for example by offset printing, ontop of the white color by use of a wet print. (It is not possible todust the design in the form of a dry powder as the dust would cling tothe white leaving a stain on the non-design portion of the decal afterfiring.) Such a design can be fired on a transparent glass: The whitebackground is necessary since offset printing does not depositsufficient color to provide opaqueness on transparent glass. In place ofthe white color, it is also possible to employ a silk screen flux.

A further advantage'of the method invention is that the decal therebyproduced can include dark colors printed on lighter colors, which is notnow possible.

It will be appreciated that the present description has been by way ofexample only and is not intended as a limitation to the scope of theinvention.

I claim:

1. A method for the preparation of an overglaze ceramic decalcomania,which comprises forming a wet ink formulation free of glass andconsisting essentially of a liquid printing medium or vehicle and anoxide coloring agent, wet printing said wet ink formulation on adecalcomania backing sheet to form a wet design layer thereon free ofglass, and separately depositing on said wet design layer a colorlessprotective coating consisting essentially of a prefused glass flux, sothat when the backing sheet, having deposited thereon the wet designlayer and protective coating, is positioned on a glazed piece of wareand fired, the protective coating of prefused glass flux fuses andtightly binds the design layer to the ware and does not mask the colorof the design layer.

2. The method in accordance with claim I, which comprises forming thewet ink formulation by mixing the coloring agent in a wet printingmedium of drying oils, varnishes or resins.

3. The method in accordance with claim 1, wherein the protective coatingconsists essentially of prefused glass and pigment, prefused glass inprinting varnish or prefused glass and pigment in printing varnish.

4. The method in accordance with claim 1, wherein the prefused glassflux is applied over the wet design by silk screening or offsetprinting.

5. The method in accordance with claim 1, wherein the design layerformed has a thickness within the range of from about 2 to about 8microns.

6. The method in accordance with claim 1, wherein the ratio of thicknessof the glassprotective coating to the design layer is within the rangeof from about 2:1

to about 3.5:1.

2. The method in accordance with claim 1, which comprises forming thewet ink formulation by mixing the coloring agent in a wet printingmedium of drying oils, varnishes or resins.
 3. The method in accordancewith claim 1, wherein the protective coating consists essentially ofprefused glass and pigment, prefused glass in printing varnish orprefused glass and pigment in printing varnish.
 4. The method inaccordance with claim 1, wherein the prefused glass flux is applied overthe wet design by silk screening or offset printing.
 5. The method inaccordance with claim 1, wherein the design layer formed has a thicknesswithin the range of from about 2 to about 8 microns.
 6. The method inaccordance with claim 1, wherein the ratio of thickness of theglass-protective coating to the design layer is within the range of fromabout 2:1 to about 3.5:1.